It is know that sodium chlorite aqueous bleaching baths can be used effectively for the bleaching of textile fibers and other organic materials. The bleaching action resides in the oxidizing effect of the various chlorine compounds which are generated and, as need arises, from the nascent oxygen which is formed by decomposition of the chlorite in acid milieu.
This composition can be effected in a cold state, i.e. at room temperature or temperatures therebelow, by direct acidification of this solution or by the introduction into the latter of reducing compounds such as formaldehyde. The decomposition is brought about practically instantaneously upon the introduction of the activator (acid or aldehyde) into the chlorite solution. The baths yellow rapidly and give rise to a rapid release of the chlorine derivatives. The oxidizing action of the chlorite baths activated cold under these conditions is excessive and generally too rapid for commercial use in the bleaching of textile fibers which requires the ability to control the process over a relatively prolonged period of time to obtain uniform and reproducible results.
It is thus esential that a bleaching bath possess a certain stability beyond the moment of preparation, especially if the process is to be carried out in a normal operating line of a textile plant. Furthermore, for health and safety reasons, it is not possible to permit chlorine dioxide, of high toxicity, to be released freely into the atmosphere as frequently occurs with conventional activators for a cold bleaching bath.
Most of the current processes for the bleaching of textile materials using sodium chlorite baths thus operate at elevated temperatures in the presence of activators for the decomposition of the chlorite. The conjoint action of the elevated temperature, usually between 70.degree. and 90.degree. C., and the activation agents permit the decomposition of the chlorite to be progressive and controlled, guaranteeing uniform bleaching.
However, this decomposition is practically always accompanied by release of chlorine compounds, more specifically chlorine dioxide, of high toxicity. Apart from their toxicity and the toxicity of other released chlorine compounds, the chlorine compounds have been found to manifest a corrosive activity upon the materials generally used for the construction of the textile machines. Thus it is necessary to provide materials, vats, vapor-collection chambers and the like, specifically adapted to resist corrosive attack.